Physiological Effects of Natural or Contaminating Compounds in a Rodents Microenvironment

Kurtz, David

Abstract

The Quality Assurance Laboratory (QAL) in the Comparative Medicine Branch at the National Institute of Environmental Health Science (NIEHS)performs testing on the microbiological and/or chemical contamination of critical aspects of the overall NIEHS research program. Our primary task is monitoring the animal research program for microbiological and/or chemical contamination that may affect animal health and welfare, as well as, the physiological responses of animals used in research studies. Our research focuses on the physiological effects of natural or contaminating compounds in the micro-environment (e.g., animal feed, caging, bedding, water, etc.)of the research animals. Our goal is to assure that we minimize exposure to environmental compounds that may effect animal health and welfare or alter physiological responses of the animals resulting in unacceptable variability. Historically, QAL studies have focused on the potential for endocrine-disrupting compounds (EDCs) being present in the micro-environment of the research animals and the impact these compounds may have on study outcomes, especially reproductive development. For these studies, pre-pubertal CD-1 mice are weaned at post-natal day (PND) 15 and given test compounds orally (via diet, water or gavage) from PND 15 to PND 35 or until vaginal opening (VO) occurs which is a developmental milestone affected by hormones. We have shown that natural phytoestrogens (e.g., daidzein and genistein) present in commercially available rodent diets or added to diets free of these compounds can significantly (P less than 0.01) accelerate the time of VO in CD-1 mice. We have also shown that the total metabolizable energy (ME) in the diet can significantly affect these hormone-sensitive endpoints, although the predictability of this variable was less powerful than the phytoestrogen content. We have shown that the estrogenic mycotoxin zearalenone is ubiquitious in commercially available corn-cob bedding. 154 of 189 (84%) of the samples were naturally contaminated with zearalenone at levels ranging from 100 to 7,000 ppb (mean 500 ppb). We have shown that levels of 5-10 ppm can significantly advance the time of VO in immature CD-1 haired and SKH-1 hairless mice. We are currently performing studies looking at the effects of autoclave sterilization of rodent feed on the physical and chemical properties of the feed. Sterilization of rodent feed is important to prevent the introduction of microorganisms that may alter animal health or physiological response, and autoclave sterilization is a widely used method. Previous studies found that autoclaving rodent feed resulted in the production of acrylamide, as does any high starch containing food (e.g., potatoes, breads, etc.). These studies also determined that the levels of acrylamide produced by autoclaving the feed were high enough to cause measurable genotoxic effects (DNA adducts). Our study determined that increasing the sterilization temperature used resulted in an increase in the harness of the pelleted feed, as well as, the concentration of acrylamide. We are currently measuring the in-vivo effects of these levels of acrylamide.